1. Field of the Invention
The present invention relates to a method of manufacturing magnetic tape and, more particularly, to a method of manufacturing magnetic tape such as tape for computer data backup, audiotape and videotape.
2. Description of the Related Art
In a method of manufacturing various types of magnetic tape such as tape for computer data backup, audiotape and videotape, a wide web-like magnetic tape material wound in roll form is drawn out from the delivery side, and slit into a plurality of narrow magnetic tapes by use of a slitter while being transported, and the magnetic tapes are wound on cores on the winding side.
As shown in FIG. 2, a conventional slitter used in the manufacturing of magnetic tapes is a device 14 that slits a wide web-like magnetic tape material 20 into a plurality of magnetic tapes 26 by use of pairs of upper and lower rotary blades. The rotary blades are generally constituted by a plurality of rotary blades 30 formed as bed knives in roller form and a plurality of rotary blades 32 in thin disk form, which perform slitting by giving a shearing force to the magnetic tape material 20 between the rotary blades 30 and the rotary blades 32.
However, when the magnetic tape material 20 is slit by the slitter 14, the side surfaces of the magnetic tapes 26 cannot be precisely cut, so that projections often occur in the edge portions of the side surfaces. FIG. 3 is an enlarged fragmentary view of FIG. 2 and shows the positional relationship between the magnetic tapes 26 and a pair of upper and lower rotary blades 30 and 32. FIG. 4 is an enlarged sectional view showing the sectional shape of the right and left side surfaces of the magnetic tape 26. The magnetic tape 26 is composed of two layers, i.e., a magnetic layer 26A on the front side and a nonmagnetic backing layer 26B on the back side. In FIGS. 2, 3 and 4, the running direction of the magnetic tape 26 is perpendicular to the drawing sheets.
Since the magnetic tapes 26 are made by slitting the magnetic tape material 20 in a stretched sate with the upper rotary blades 32 as shown in FIG. 3, each of the edge portion of the magnetic layer 26A at an upper right part and the edge portion of the nonmagnetic layer 26B at a lower left part in FIG. 4 has a projection, and each portion of adjacent magnetic tapes 26 corresponding to the projection has a nick. Therefore, the section of the magnetic tape 26 as a whole assumes a roughly parallelogrammatic shape.
When the magnetic tape 26 has such a sectional shape, the projections are often scraped off the magnetic tape 26 during a run on a tape deck, and dust produced from the removed projections causes troubles such as signal dropout (DO) and clogging of the head in the tape deck. Although such troubles have so far been coped with by measures such as optimization of the setting conditions of the slitter, etc., a fundamental solution has not been reached and there has been a strong requirement for improvement.